Because of the recent striking increase in the incidence of clear-cell adenocarcinoma of the lower genital tract in young females as a result of prenatal exposure to diethylstilbestrol (DES), the Registry of Clear-cell Adenocacinoma of the Genital Tract in Young Females has been established to investigate in depth the epidemiology, clinicopathologic features, and therapy of these tumors. All cases of clear-cell adenocarcinoma of the genital tract in females born after 1940 are being investigated in detail whether or not there is a history of maternal medication. In addition all other types of vaginal cancer occurring in young females and associated with maternal hormonal therapy are being studied. Cases are entered in the Registry from throughout the world. Through yearly follow-up of all accessioned cases, detailed evaluation of sites and therapy of tumor recurrences as well as mechanisms of death, autopsy data, etc., are recorded. These studies should establish the natural history of the disease, its optimal therapy, and the role of DES and possibly other hormones in the pathogenesis of these cancers. The precancerous potential of vaginal adenosis is also being investigated in the Registry material as well as by examination and follow-up of asymptomatic DES-exposed females. BIBLIOGRAPHIC REFERENCES: Herbst, A. L., Scully, R. E., Robboy, S. J., Poskanzer, D.C., and Ulfelder, H.: Stilbestrol-induced abnormalities of the genital tract in young women. In: Progress in Gynecology, Vol. 6. Eds: M. L. Taymor and T. H. Green. Grune and Stratton, 1975. Herbst, A. L., Scully, R. E., and Robboy, S.J.: The significance of adenosis and clear-cell adenocarcinoma of the genital tract in young females. J. Reprod. Med. 15: 5-11, 1975.